The present invention relates to a magnetic recording and reproducing head which can magnetically write and optically read out, and more particularly to a single pole magnetic head of write and read out composite type which is suitable to effect writing and reproducing by means of a single head.
As recording/reproducing systems with high recording density, there are known a perpendicular magnetic recording and reproducing system and a magneto-optical writing and reproducing system. Further, there is also known a recording/reproducing system using a perpendicular magnetic head in recording and an optically read-out head utilizing magneto-optic effect in reproducing, with coupled use of the advantages of both systems.
Heretofore, as a method for optically reproducing magnetized information from a recording medium by means of a magneto-optic effect (Faraday effect, Kerr effect and the like) by magnetically transferring it on a high permeability magnetic film perpendicularly disposed in close adjacency of a medium surface, there can be found a disclosure in the Japanese Patent Application Laid-Open, No. 1244/72 which is based upon U.S. Pat. No. 3,665,431. In case when such a device is used as a head for exclusive use in reproducing, a thin film material with large magneto-optical effect is sufficient to be used as a high permeability thin film, and can display a sufficient characteristic as a single layer. However, in order to write and reproduce at high speed in a magnetic disc apparatus, a magnetic tape device and the like, a structure should be devised which is capable to write and read out with the same head. In this respect, the above-mentioned example lacked the consideration on the function as a head for writing use.
On the other hand, in a prior art optically reproducing type single pole magnetic head shown in FIG. 1, capable of writing and reproducing with the same head, a high permeability magnetic thin film 1 of the main pole was divided into two, and further there was arranged a second magnetic thin film 2, which had an easy magnetization axis in a direction perpendicular to the film surface and was closely adhered thereto, as described in the Japanese Patent Application Laid-Open, No. 169946/82. Thus, a polarized laser beam 9 was irradiated perpendicularly to this second thin magnetic film and the magnetized state of the main pole was discriminated by a the polar Kerr effect, the Faraday effect by perpendicularly incident optical beam, and the like. That is, the reproduction of high density recording was effected by converting the magnetization induced in the main pole from the magnetic medium into the difference of the strength of light. However, in this method, as shown in FIG. 1, since the second magnetic thin film 2 is a perpendicular magnetizable film, almost all of the magnetic flux 4 in the magnetic circuit goes out from the magnetic circuit in the surface of the second magnetic thin film. Therefore, in such a construction, the magnetic circuit of the main pole becomes to have a large open end, and even when the magnetized state of the main pole is required to be reversed in dependence with a magnetic signal, it is necessary to expend extremely large energy. That is, it becomes difficult to let the magnetized state of the main magnetic pole faithfully follow the magnetic signal from the medium. As described above, in the above-described latter example, there lacked the consideration on the magnetic circuit construction for making an optical reproducing head with a high sensitivity.
In FIG. 1, the symbol 3 designates the direction of magnetization, 5 the recording medium, 6 a substrate of the recording medium, 7 an auxillary magnetic pole and 8 a coil for writing.